During the coming year using a sheep fetal animal model, studies will be done of the regulatory mechanism of fetal cerebral blood flow. The model as mentioned will be an intrauterine fetal sheep of approximately 130 days' gestation. Flow to the central nervous system will be measured using a combination of flow probes and microspheres. Controlling mechanisms to be studied include low oxygen and high oxygen as well as various steroids to include estrogen and progesterone.